How to know that a form was created? - delphi

Question

I want to find a way to know that a form was created at run time (or destroyed).
This for Delphi or fpc.
Many thanks
PS : Is there a way to retrieve that info for all objects ?

Answer 1

I want to have a event that tells me that a new object was just created at run time (or destroyed).
There are no built in events that fire whenever an object is created or destroyed.
Because I like writing code hooks, I offer the following unit. This hooks the _AfterConstruction method in the System unit. Ideally it should use a trampoline but I've never learnt how to implement those. If you used a real hooking library you'd be able to do it better. Anyway, here it is:
unit AfterConstructionEvent;
interface
var
OnAfterConstruction: procedure(Instance: TObject);
implementation
uses
Windows;
procedure PatchCode(Address: Pointer; const NewCode; Size: Integer);
var
OldProtect: DWORD;
begin
if VirtualProtect(Address, Size, PAGE_EXECUTE_READWRITE, OldProtect) then
begin
Move(NewCode, Address^, Size);
FlushInstructionCache(GetCurrentProcess, Address, Size);
VirtualProtect(Address, Size, OldProtect, #OldProtect);
end;
end;
type
PInstruction = ^TInstruction;
TInstruction = packed record
Opcode: Byte;
Offset: Integer;
end;
procedure RedirectProcedure(OldAddress, NewAddress: Pointer);
var
NewCode: TInstruction;
begin
NewCode.Opcode := $E9;//jump relative
NewCode.Offset := NativeInt(NewAddress)-NativeInt(OldAddress)-SizeOf(NewCode);
PatchCode(OldAddress, NewCode, SizeOf(NewCode));
end;
function System_AfterConstruction: Pointer;
asm
MOV EAX, offset System.#AfterConstruction
end;
function System_BeforeDestruction: Pointer;
asm
MOV EAX, offset System.#BeforeDestruction
end;
var
_BeforeDestruction: procedure(const Instance: TObject; OuterMost: ShortInt);
function _AfterConstruction(const Instance: TObject): TObject;
begin
try
Instance.AfterConstruction;
Result := Instance;
if Assigned(OnAfterConstruction) then
OnAfterConstruction(Instance);
except
_BeforeDestruction(Instance, 1);
raise;
end;
end;
initialization
#_BeforeDestruction := System_BeforeDestruction;
RedirectProcedure(System_AfterConstruction, #_AfterConstruction);
end.
Assign a handler to OnAfterConstruction and that handler will be called whenever an object is created.
I leave it as an exercise to the reader to add an OnBeforeDestruction event handler.
Note that I am not saying that such an approach is a good thing to do. I'm just answering the direct question that you asked. You can decide for yourself whether or not you want to use this. I know I would not do so!

Answer 2

Use TForm's OnCreate event to inform whoever you want in whatever way you want.

Answer 3

In MS Windows you can hook events of your process using this small template:
{$mode objfpc}{$H+}
uses
Windows, JwaWinUser;
function ShellProc(nCode: longint; wParam: WPARAM; lParam: LPARAM): longint; stdcall;
var
wnd: HWND;
begin
Result := 0;
case nCode of
HSHELL_WINDOWCREATED:
begin
wnd := wParam;
// Check window
// Get task handle
// Get window icon
// Add task to the list
// Call event
end;
HSHELL_WINDOWDESTROYED:
begin
wnd := wParam;
// Check window
// Get task handle
// Get window icon
// Remove task to the list
// Call event
end;
HSHELL_LANGUAGE:
begin
// Get language
// Call event
end;
HSHELL_REDRAW:
begin
// Call event
end;
HSHELL_WINDOWACTIVATED:
begin
// Get language
// Call event
end;
//HSHELL_APPCOMMAND:
//begin
// { TODO 1 -ond -csys : Specify return value for this code }
// Result := -1;
//end;
end;
// Call next hook in the chain
Result := CallNextHookEx(
0,
nCode,
wParam,
lParam);
end;
var
FCallbackProc: HOOKPROC;
function InitShellHook(AProc: HOOKPROC): HHOOK; stdcall; export;
begin
FCallbackProc := AProc;
Result := SetWindowsHookEx(WH_SHELL, #ShellProc, 0, 0);
end;
procedure DoneShellHook(AHook: HHOOK); stdcall; export;
begin
UnhookWindowsHookEx(AHook);
end;
HSHELL_WINDOWCREATED will inform you that your process was create new window.
Call InitShellHook with your procedure address (see HOOCPROC declaration).